The present invention relates to a system for controlling the cruising speed of a vehicle, the instantaneous speed of which depends on the degree of opening of a throttle valve on the vehicle feed system, e.g. the fuel throttle or a throttle-controlled body on the injection system.
Particularly on long journeys or when strict speed limits apply, considerable advantage is afforded by automatic devices designed to maintain a predetermined speed with no action required by the driver on the accelerator pedal. Various types of such devices, commonly referred to as "cruise controls", are known:
Patent application No. EP-A-0234490 relates to a device featuring a geared motor for controlling both opening and closing of the throttle. This device is both complex and expensive, due to two-way operation of the electric motor for opening and closing the throttle, and the potentiometer employed for controlling the motor. PA1 U.S. Pat. No. 4,725,969 relates to a similar device, i.e. featuring a geared motor for both opening and closing the throttle, but which also features a delicate high-cost electromagnetic clutch for disabling the system. PA1 Pat. No. DE-B-1214103 relates to a further device featuring a geared motor for controlling both opening and closing of the throttle, as well as complex high-cost components such as a potentiometer and electromagnetic clutch.
In addition to those mentioned above, a major drawback of known powered devices of the aforementioned types is that, in the event of power failure to the geared motor, and in the absence of an electromagnetic clutch, the throttle may lock or at any rate become difficult to operate directly via the accelerator pedal, the danger of which in terms of driving safety is only too obvious.